Imaging tissue mechanical properties using impulsive acoustic radiation force

Acoustic radiation force impulse (ARFI) imaging utilizes brief, high energy, focused acoustic pulses to generate radiation force in tissue, and conventional diagnostic ultrasound methods to detect the resulting tissue displacements in order to image the relative mechanical properties of tissue. Parametric images of maximum displacement, the time the tissue takes to reach its peak displacement, and tissue recovery time provide information about tissue material properties and structure. FEM simulations have been developed and validated of tissue mechanical and thermal response to ARFI excitation. Potential clinical applications under investigation include: soft tissue lesion characterization, assessment of diffuse and focal atherosclerosis, and imaging of thermal lesion formation during tissue ablation procedures. In both in vivo and ex vivo data, structures shown in matched B-mode images are in good agreement with those shown in ARFI displacement images. In ex vivo tissue ablation studies (HIFU and RF-ablation), thermal lesion size correlates well with matched pathology images. In vivo breast studies, palpable breast masses exhibit smaller displacements (i.e. they are stiffer) than surrounding tissues. Some malignant masses appear larger in ARFI displacement images than in matched B-mode images, consistent with a desmoplastic reaction; however, this is not the case for all malignant breast masses that have been studied. Benign fibroadenomas, in general, exhibit less contrast than malignant masses in ARFI displacement images. Results from ongoing studies will be presented.